Bardet-Biedl syndrome (BBS) is a rare genetic disease that causes retinal degradation, obesity, kidney dysfunction, polydactyly, and other cilium-related disorders. To date, more than 20 BBS genes, whose mutants cause BBS phenotypes, have been identified, and eight of those (BBS1-2, 4-5, 7-9, and 18) are known to form the BBSome complex. Recent studies have revealed that the BBSome is closely involved in the trafficking of signaling proteins in the primary cilium. Mutations in BBS genes are highly pathogenic because trafficking in the primary cilium is not fully functional when BBS mutations impair assembly of the BBSome. However, the functional links between onset of BBS and BBSome assembly are not well understood. To address this gap in knowledge, we examined the structure of a BBSome assembly intermediate, the BBSome core complex (BBS2, 7, and 9). We employed a combination of chemical crosslinking coupled with mass spectrometry (XL-MS) and electron microscopy (EM) to determine the structure. We applied this structural information to BBS mutations in the core complex to understand how these mutations might cause the disease. These results provide the first structural model of the BBSome core complex and give insight into the molecular basis of Bardet-Biedl syndrome. We have also investigated the mechanism of assembly of the two mTOR kinase complexes (mTORC1 and 2). mTOR is a master regulator of cell metabolism, growth and proliferation. As such, mTOR is a high-value drug target. We investigated the mechanism of assembly of these mTOR complexes and found that the cytosolic chaperonin CCT contributes to mTOR signaling by assisting in the folding of mLST8 and Raptor, components of mTORC1 and mTORC2. To understand the function of CCT in mTOR complex assembly at the molecular level, we have isolated the mLST8-CCT complex and performed a structural analysis using chemical cross-linking couple with mass spectrometry (XL-MS) and cryogenic EM. We found that mLST8 binds CCT deep in its folding cavity, making specific contacts with the CCTα and γ subunits and forming a near-native β-propeller conformation. This information can be used to develop new therapeutics that regulate mTOR activity by controlling mTOR complex assembly.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





BBS, primary cilia, BBSome core complex, EM, XL-MS, CCT, mTORC, PhLP1



Included in

Chemistry Commons